This invention relates to novel data communication cables, and more particularly to high speed data communication cables with reduced cross-talk.
Over the last decade, the deployment of computer networks has steadily increased, which in turn increased the demand for data communication cables. The performance requirements imposed on new communication cables also increased steadily with the development of new network architectures. Initially, conventional telephone-grade cables were used for voice transmission and for low speed data transmission in the range of a few megabits per second. Unshielded twisted pairs have been used to transmit data in local area networks (LANs). However, such cables were inadequate for high speed transmissions. Therefore, new types of data cables have been developed and introduced.
Present network architectures, such as 100Base-T and 1000Base-T, require high speed communication cables with low attenuation, acceptable return loss, low crosstalk and good electromagnetic compatibility (EMC) performance. These parameters ensure a substantially bit-error free data transmission. Modern high speed data grade cables utilize twisted pairs of insulated conductors. These cables must meet specific requirements with respect to attenuation, cross-talk, impedance, return loss, delay, delay skew and balance. The available performance margin for a data grade cable is indicated by its attenuation to crosstalk ratio (ACR) and equal level far end cross-talk (EL FEXT). ACR is calculated by subtracting the attenuation of the disturbing pair from the near-end cross-talk (NEXT) in dB. EL FEXT on the far side is calculated by subtracting the attenuation of the disturbing pair from the far-end cross-talk (FEXT). The cross-talk depends inversely on the square of the distance of the twisted pairs.
Modern network architectures use simultaneous transmission of data over several twisted pairs, and may even use 1000Base-T simultaneous, bi-directional transmission over four pairs of one cable. Thus data communication cables used for these protocols have to have very good NEXT and FEXT performance. The required performance is so high, that crosstalk arising from adjacent cables may become detrimental to the high speed data transmission. Such a crosstalk is referred to as alien crosstalk, since it is generated by alien influences outside the considered cable.
The near-end cross-talk in one twisted pair arises from the neighboring xe2x80x9cdisturbingxe2x80x9d pairs inside the same cable. This coupling is inversely proportional to the square of the distance of the centerline of the disturbed and disturbing twisted pairs. Round cables with several twisted pairs have a varying distance between the pairs with the same twistlay. This variation occurs since the mean center to center distance, between pairs with substantially equal twistlay, is in the order of the diameter of the cable. Hence, the crosstalk between such pairs is relatively weak, despite the fact that one should expect relatively poor crosstalk performance due to the same twistlay length.
There is a way to compensate for the cross-talk coupled within the same cable because the coupling is common mode. Since the two conductors of each twisted pair carry complementary signals, the cross-talk coupled within the same cable can be compensated by adaptive amplifier techniques. However, the alien cross-talk, coupled from the outside of the cable into a twisted pair, is statistical and thus cannot be compensated for.
Therefore, there is still a need for high speed data communication cables with very low cross-talk arising from neighboring pairs of twisted conductors and cables with very low alien cross-talk.
The present invention is directed to high speed data communication cables with optimal cross-talk performances. According to one aspect, a data communication cable includes a cable jacket surrounding a plurality of twisted pairs of insulated conductors disposed over a length of the communication cable in an arrangement that reduces cross-talk between the twisted pairs. The cable also includes a first region having a first thickness disposed between two regions having a second thickness.
According to another aspect, a data communication cable includes a cable jacket surrounding a plurality twisted pairs of insulated conductors extending side-by-side over a length of the cable with the adjacent twisted pairs having different non-parallel lays. The cable assembly has a non-uniform outer width dimension that precludes aligned stacking of a plurality of the cable assemblies.
According to another aspect, a data communication cable includes several twisted pairs of insulated conductors arranged side-by-side, and a cable jacket surrounding the twisted pairs and having a substantially flat profile. A structure located on the outer surface of the jacket is arranged to prevent symmetric stacking of several communication cables with such substantially flat profile thereby reducing alien cross-talk arising from outside of the communication cable. The structure may have a rectangular, trigonal, oval shape (or a similar shape) and may be located outside of the cable jacket over the entire length of the cable.
Preferred embodiments of these aspects include one or more of the following features.
The communication cable may have a profile with regions of two thicknesses wherein the first thickness is less than the second thickness. Alternatively, the first thickness may be greater than the second thickness. The first region may be substantially flat. The communication cable may have two regions of the second thickness and these regions may have a semi-circular cross-section. Alternatively, the two regions of the second thickness may have a substantially flat cross-section. The two regions of the second thickness may have a substantially polygon-shaped cross-section.
The communication cable may include sheathing elements each surrounding the twisted pair of insulted conductors. The sheathing element may be made of a dielectric material or a conducting material. The conducting material may be a conducting foil or another metallic material.
The communication cable further includes a plurality of inwardly extending fins that are at least partially disposed between the individual twisted pairs. The fins may form a plurality of channels, wherein each channel is arranged to receive one twisted pair of insulated conductors. The fins may form an integral part of the cable jacket.
Advantageously, the novel communication cable achieves very high cross-talk performance by providing an essentially flat cable design, which has reduced cross-talk resulting from the side-by-side position of its twisted pairs, and includes novel structures formed on the outer periphery of the cable jacket. The novel structures prevent completely random stacking of the cables or increase the average pair to pair distance of pairs with the same twist lay. When the novel cables are located together in a tray, conduit, trough or plenum, the jacket structures also prevent parallel, uniform stacking of the cables and thus prevent alignment of twisted pairs with same twist lay.